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Fever (Elevated Temperature)

What is Fever (elevated temperature)?

Fever, medically termed pyrexia, is a temporary increase in body temperature above the normal daily range. In adults, a temperature ≥ 100.4 °F (38 °C) is generally considered a fever; in children, the threshold may be slightly lower depending on the measurement site (oral, rectal, axillary, or ear). Fever is not a disease itself—rather, it is a sign that the body’s internal thermostat (the hypothalamus) has been reset in response to an underlying trigger such as infection, inflammation, or certain medications.

Fever is a natural defense mechanism. Raising the body’s temperature can inhibit the replication of many pathogens and enhance the activity of immune cells, including white blood cells and interferons. However, very high or prolonged fevers can be harmful, especially in infants, the elderly, or people with chronic medical conditions.

Common Causes

Fever can be triggered by a wide variety of conditions. The most frequent causes include:

• Viral infections – influenza, COVID‑19, respiratory syncytial virus (RSV), dengue, and viral gastroenteritis.
• Bacterial infections – pneumonia, urinary tract infection, strep throat, meningitis, and cellulitis.
• Parasitic infections – malaria, toxoplasmosis, and giardiasis.
• Inflammatory diseases – rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease.
• Heat‑related illnesses – heat exhaustion or heat stroke when the body cannot dissipate heat.
• Medications – drug fever from antibiotics, antiepileptics, or allopurinol, and fever as a side‑effect of vaccines.
• Neoplastic conditions – lymphomas, leukemias, and solid tumors often manifest with periodic fevers.
• Endocrine disorders – hyperthyroidism can cause a low‑grade persistent fever.
• Autoimmune reactions – fever of unknown origin (FUO) may result from an undiagnosed autoimmune process.
• Recent surgery or trauma – tissue injury releases cytokines that may raise temperature.

Associated Symptoms

The presence of fever often coincides with other signs that help point toward the underlying cause. Common accompanying symptoms include:

• Chills or rigors
• Sweating
• Headache
• Muscle or joint aches (myalgia)
• Fatigue and generalized weakness
• Loss of appetite
• Dehydration (dry mouth, reduced urine output)
• Specific organ‑related symptoms (e.g., cough with pneumonia, dysuria with urinary tract infection, abdominal pain with gastroenteritis)

When to See a Doctor

Most short‑lived fevers resolve on their own, but certain scenarios warrant prompt medical evaluation:

• Infants younger than 3 months with a temperature ≥100.4 °F (38 °C) or any fever in a newborn < 28 days.
• Fever lasting > 48 hours in adults or > 72 hours in children without clear cause.
• Temperature ≥ 105 °F (40.5 °C) at any age.
• Severe headache, stiff neck, or altered mental status (possible meningitis).
• Persistent vomiting, severe diarrhea, or inability to keep fluids down.
• Rash that spreads quickly, especially if accompanied by fever (possible meningococcemia or allergic reaction).
• Chest pain, shortness of breath, or difficulty breathing.
• Signs of dehydration (dry mucous membranes, scant urine, dizziness).
• Underlying chronic disease (e.g., heart failure, COPD, immunosuppression) with new fever.
• Any fever in a pregnant woman, especially after the first trimester.

Diagnosis

History and Physical Examination

Doctors begin with a detailed history, asking about:

• Onset, pattern and highest measured temperature.
• Recent travel, exposures, sick contacts, vaccinations.
• Associated symptoms (cough, pain, urinary changes, rash).
• Medication use, including over‑the‑counter drugs and supplements.
• Past medical history (immunosuppression, chronic illnesses).

A thorough physical exam looks for focal signs of infection (e.g., lung crackles, abdominal tenderness, joint swelling) and for systemic clues such as lymphadenopathy or a rash.

Laboratory and Imaging Studies

• Complete blood count (CBC) – identifies leukocytosis, leukopenia, or anemia.
• Blood cultures – indicated for high‑grade fever, sepsis suspicion, or fever > 72 h without source.
• Urinalysis & urine culture – common source in adults and children.
• Chest X‑ray – evaluates pneumonia or other thoracic pathology.
• Serologic or PCR testing – for viral infections (influenza, SARS‑CoV‑2, EBV, CMV).
• Stool studies – if gastrointestinal symptoms dominate.
• Inflammatory markers (CRP, ESR) – helpful in assessing autoimmune or inflammatory causes.
• In selected cases, CT/MRI or lumbar puncture may be necessary (e.g., suspected meningitis or intra‑abdominal abscess).

Treatment Options

General Principles

Treatment aims to (1) address the underlying cause, and (2) alleviate discomfort while preventing complications.

Pharmacologic Management

• Antipyretics – Acetaminophen (paracetamol) 500–1000 mg PO q4‑6 h (max 4 g/day) or ibuprofen 200–400 mg PO q6‑8 h (max 1.2 g/day). Both lower hypothalamic set‑point and relieve aches.
• Antibiotics – Reserved for confirmed or strongly suspected bacterial infections. Choice guided by local resistance patterns; e.g., amoxicillin for streptococcal pharyngitis, ceftriaxone for meningitis.
• Antiviral agents – Oseltamivir for influenza, remdesivir or paxlovid for COVID‑19, when indicated.
• Antimalarial therapy – Artemisinin‑based combination therapy for confirmed malaria.
• Corticosteroids – May be used in certain inflammatory or autoimmune fevers (e.g., lupus flare).

Supportive Care

• Maintain adequate hydration – oral rehydration solutions or intravenous fluids for severe dehydration.
• Rest in a cool, comfortable environment; light clothing and a damp washcloth can aid heat loss.
• Nutrition – small, frequent meals; consider nutrient‑dense soups.
• Monitor temperature every 4–6 hours to assess response to treatment.

Special Situations

• Infants – Prompt evaluation; antipyretics are often given while awaiting assessment.
• Elderly – Lower fever thresholds may be significant; watch for delirium.
• Immunocompromised – Low‑grade fevers can herald serious infection; early empiric broad‑spectrum antibiotics may be required.

Prevention Tips

• Practice good hand hygiene – wash hands for at least 20 seconds with soap.
• Stay up‑to‑date with vaccinations (influenza, COVID‑19, pneumococcal, MMR, varicella).
• Use insect repellent and netting in malaria‑endemic areas; seek prophylactic antimalarial meds when traveling.
• Cook meats thoroughly and wash fruits/vegetables to prevent food‑borne infections.
• Avoid close contact with people who are visibly ill; wear masks during outbreaks of respiratory viruses.
• Maintain a healthy lifestyle – balanced diet, regular exercise, adequate sleep – to strengthen immune function.
• Review all medications with your pharmacist or physician; some drugs can cause drug‑induced fever.

Emergency Warning Signs

References

1. Mayo Clinic. “Fever.” https://www.mayoclinic.org. Accessed May 2026.
2. Centers for Disease Control and Prevention. “Fever and Its Management.” CDC, 2023. https://www.cdc.gov.
3. National Institutes of Health. “Fever of Unknown Origin (FUO).” NIH Clinical Guidelines, 2022. https://www.ncbi.nlm.nih.gov.
4. World Health Organization. “Management of Severe Acute Respiratory Infection When COVID‑19 Is Suspected.” WHO, 2021. https://www.who.int.
5. Cleveland Clinic. “When to Call the Doctor for a Fever.” Cleveland Clinic, 2024. https://my.clevelandclinic.org.

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